Foliar-applied pesticidal and plant growth modifying chemicals are widely used in agricultural, industrial, recreational and residential areas worldwide. These chemical agents illustratively include insecticides, fungicides, herbicides, plant growth regulators and plant nutrients among other chemicals. Such chemicals are typically applied by spraying on the foliage of vegetation to be protected, controlled, killed or modified, but other methods such as rope-wick application are known. Some of these agents show contact action, killing, controlling or modifying the growth of target organisms at the site of deposition. Other chemicals are systemic, translocating within the plant to a site of action remote from the site of deposition. Still other chemicals show both contact and systemic action.
A common concern with several such chemicals is that efficacy can be reduced if rain falls shortly after spraying or other mode of application. This concern is more pronounced with chemicals that have moderate to high solubility in water. Many methods of overcoming the problem of reduced efficacy due to rain have been disclosed. Such methods are said to have the aim of enhancing "rainfastness" of foliar-applied agents.
Methods to enhance rainfastness include addition to the spray solution of oils or other lipophilic substances, polymers and other materials which are alleged to enhance spreading and sticking of the applied formulation to leaves, and addition of various surfactants. Among surfactants which have been disclosed for rainfastness enhancement are organosilicone copolymers, for example the ethoxylated siloxane Silwet L-77 of Union Carbide Corporation. Such surfactants, as well as other spray additives used to enhance rainfastness, tend to be relatively expensive and many have other drawbacks.
Alternatively, a rainfastness enhancing material may be provided by the manufacturer or supplier of the foliar-applied pesticidal or plant growth modifying agent as an ingredient in the formulation of said agent.
An example of a foliar-applied agent whose efficacy is sensitive to the occurrence of rain shortly after application is the herbicide N-phosphono-methylglycine, also known by its common name glyphosate.
Glyphosate is a highly effective and commercially important herbicide useful for combating the presence of a wide variety of unwanted vegetation, including agricultural weeds. Glyphosate is applied as a formulated product to the foliage of annual and perennial grasses and broadleaf plants and the like, and is taken up over a period of time into the leave whence it translocates throughout the plant.
Glyphosate in ionic form has relatively high water solubility, especially when formulated as a salt, and during the uptake period immediately after application glyphosate is vulnerable to being washed off the foliage by rain or by overhead watering or irrigation. As glyphosate has practically no herbicidal activity in the soil, its efficacy is seriously reduced by such washing.
The length of time during which glyphosate is somewhat vulnerable to rain depends on many environmental and plant factors, and on the duration and intensity of rain, but can be as short as thirty minutes or as long as twelve hours or more after application. In the great majority of cases rain falling six or more hours after application does not seriously affect performance of the herbicide.
Usually, glyphosate is formulated in commercial compositions in the form of a water-soluble salt. Salts in commercial use include alkylamine salts, such as the isopropylamine salt, alkali metal salts, such as the sodium salt, the ammonium salt and the trimethylsulfonium salt. However, formulations of glyphosate in its acid form are also used. Typical glyphosate salt formulations include aqueous concentrates, requiting simple dilution in water for application by the end-user, and water-soluble or water-dispersible dry formulations, especially granules, requiring dissolution or dispersion in water prior to application. Most formulations, whether liquid or dry, also contain one or more surfactants. Even with such surfactants in the formulation there remains a need for enhanced rainfastness of glyphosate in many situations.
The ethoxylated siloxane surfactant Silwet L-77 referred to above has been the subject of much published research into rainfastness enhancement for glyphosate salt formulations. Its main active ingredient is 1,1,1,3,5,5,5-heptamethyltrisiloxanylpropyl-omega-methoxypoly (ethylene oxide) where the average number of ethylene oxide units is approximately seven. Other siloxanes of related composition are also described in the art. In addition to the high cost of Silwet L-77, common to all siloxanes, a number of disadvantages have been described, notably its tendency to antagonize the activity of glyphosate on some species in the absence of rain. A technical solution to this problem is provided in Australian Patent No. 609,628, wherein a humectant such as glycerin added to the spray solution overcomes the antagonism; however cost still remains a major deterrent in most situations.
A major advance in cost-effective rainfastness enhancement for glyphosate was provided in U.S. Pat. No. 5,258,354, wherein acetylenic diol surfactants, exemplified by ethoxylates of 2,4,7,9-tetramethyl-5-decyne-4, 7-diol, are shown to give rainfastness at least equal to Silwet L-77 when used in the presence of certain other surfactants, but without the occurrence of antagonism in the absence of rain. Concentrate formulations of glyphosate with such acetylenic diol surfactants are disclosed which are both chemically and physically stable over a wide range of conditions.
While acetylenic diol surfactants are obtainable at much lower cost than effective organosilicone surfactants, they could still be too costly for many applications. In most cases the end-user wishes some degree of insurance against the possibility of rain washing the herbicide off the foliage before it has had time to penetrate into the leaves. The end-user seldom knows that it will certainly rain. For such insurance purposes, economics dictate a still lower-cost adjuvant or formulation ingredient. Various low-cost surfactants have from time to time been died to give rainfastness enhancement, including ethoxylated alkylphenols such as octylphenol and nonylphenol ethoxylates. These are among the most widely used general purpose adjuvants for glyphosate in many markets, and are not considered by most users to provide reliable rainfastness enhancement.
E. H. Brumbaugh (Third International Symposium on Adjuvants for Agrochemicals, Cambridge, U.K., August 1992) showed that addition of APSA-80, a product said to contain 80% of a nonionic surfactant based on nonoxynol-9 (nonylphenol ethoxylate with an average of 9 moles ethylene oxide per mole of nonlphenol), enhanced rainfastness of glyphosate, applied as Roundup.RTM. herbicide in an ultra-low volume of water (30.6 l/ha). The adjuvant was used at concentrations ranging from 0.1% to 0.5% of the spray solution. Rainfastness improvement was not evident on all species.
There is provided herein a new method of use of alcohol alkoxylate surfactants of molecular structure defined more particularly below for enhancing the rainfastness of foliar-applied pesticidal and plant growth modifying agents.
There are also provided herein new, storage-stable, liquid or dry concentrate compositions comprising glyphosate or one or more of its salts, an alcohol alkoxylate surfactant of molecular structure defined below and one or more other surfactants, said compositions showing enhanced rainfastness by comparison with similar compositions not containing said alcohol alkoxylate surfactant, and showing at least equal rainfastness by comparison with much higher-cost compositions of the prior art based on ethoxylated siloxane or acetylenic diol surfactants. Not all alcohol alkoxylate surfactants provide the desired degree of rainfastness enhancement. Alcohol alkoxylates of molecular structure defined below, when used in accordance with the present invention, give superior rainfastness by comparison with, for example, primary linear alcohol alkoxylates or alkylphenol alkoxylates of the prior art.
Also provided herein are new, storage-stable liquid or dry concentrate compositions comprising glyphosate or one or more of its salts, an alcohol alkoxylate surfactant of molecular structure defined below and one or more other surfactants, said compositions showing enhanced herbicidal efficacy by comparison with glyphosate compositions known in the art, whether rain occurs shortly after application or not.
Among the surfactants used in combination with alcohol alkoxylates in compositions of the present invention are ethoxylated tertiary and quaternary alkylamines and alkylamine oxides.
It is known in the art that ethoxylated alkylamine or alkylamine oxide surfactants having an average alkyl chain length in the range from 10 to 20 carbon atoms and having an average of from 2 to 20 moles of ethylene oxide (EO) per mole of amine, are effective in potentiating the herbicidal activity of glyphosate compositions. European Patent No. 0 290 416, for example, discloses glyphosate compositions containing tertiary alkylamine surfactants within the range encompassed by the above description, and notes that such compositions, particularly those with EO levels in the lower part of the range mentioned above, have high herbicidal unit activity. European Patent No. 0 274 369 discloses highly efficacious glyphosate compositions containing quaternary alkylamine surfactants within the range encompassed by the above description. In both cases it is disclosed that for best performance the compositions should also contain a significant mount of an inorganic ammonium salt such as ammonium sulfate.
U.S. Pat. No. 5,118,444 discloses ethoxylated alkylamine oxide surfactants within the range encompassed by the above description, and indicates their usefulness as components of glyphosate formulations.
Ammonium sulfate is bulky and can only be accommodated in a concentrate formulation at an effective level by greatly lowering the content of active ingredient, in this case glyphosate. A significant advance in the art of formulating glyphosate concentrates would result from identification of a material which further enhances the efficacy of compositions containing ethoxylated alkylamine surfactants, but which is effective at a lower concentration than is required in the case of ammonium sulfate. That material could be incorporated in a concentrate formulation without unacceptable dilution of the glyphosate active ingredient. The present invention provides just such an advance in the art.